Abstract
Geometrically chiral plasmonic nanostructures lead to chiroptical far-field responses much stronger than those of natural chiral molecules. These signals, however, are unwanted for chiral plasmonic near-field sources, where the circular dichroism response of a chiral analyte should be enhanced. In this chapter, we introduce the concept of plasmonic racemates, which combine the strong chiral near-field response of chiral nanostructures with the zero chiroptical far-field response of achiral systems. We show that such racemates provide enantiomorphic fields under enantiomorphic illumination, which is important for straightforward spectroscopy schemes. Additionally, we discuss how to create locally chiral plasmonic lattices, which are achiral periodic arrangements of simple building blocks that build chiral substructures locally. By this means, such lattices are plasmonic racemates with a very high packing density.
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Notes
- 1.
This is even true from a geometric point of view: For each left-handed molecule, there is also a right-handed one in the mixture. Each individual molecule changes its handedness after parity inversion, but the collective superstructure of all molecules looks still the same.
- 2.
Recently, Larsen and collaborators used a GLAD technique to fabricate a plasmonic racemate. The resulting film consisted of patches with opposite handedness [4].
- 3.
This is a fact that is simply understood because the helix itself is geometrically chiral. In Chap. 7, where we will discuss highly symmetric and geometrically achiral nanoantennas, the same effect occurs. However, this behavior is much more confusing in the corresponding discussion due to the high symmetry of the system.
- 4.
It is divided by four if the more isotropic unit cell from Fig. 6.1 is assumed.
- 5.
Similar observations for gammadion-shaped planar chiral geometries have been reported in [5].
- 6.
The optimization is even more complicated due to Rayleigh anomalies , which arise from the periodic arrangement. It has been shown that they can have a strong influence on the magnitude of recorded chiroptical responses [6]. However, a detailed analysis of the influence of Rayleigh anomalies on chiral plasmonics has, to the best of our knowledge, not been carried out yet.
- 7.
Although full rotational symmetry is considered (and provided by the disks), \(C_4\) symmetry would be sufficient. Our considerations do not hold for elements that are neither \(C_4\) nor \(C_\infty \).
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Schäferling, M. (2017). Chiral Fields of Macroscopically Achiral Arrangements. In: Chiral Nanophotonics. Springer Series in Optical Sciences, vol 205. Springer, Cham. https://doi.org/10.1007/978-3-319-42264-0_6
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DOI: https://doi.org/10.1007/978-3-319-42264-0_6
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